With rapid development of the social economy, the fossil non-renewable energy, such as coal, crude oil, natural gas, oil shale and the like, is exhausted day by day, and environmental pollution caused by contaminants, such as CO2, SO2, NOx and the like, generated after the fossil non-renewable energy is burnt, is serious day by day, so that the human beings have to seriously consider energy access ways and environment improvement methods. A biomass is a renewable energy, which has huge potential and advantages in the aspects of meeting energy demands, reducing environment pollution and improving an energy structure. The biomass means all organic substances formed by directly or indirectly using the photosynthesis of green plants, including plants, animals, microorganisms and excretions and metabolites thereof, and the biomass has renewability, low pollution and wide distributivity. In recent years, conversion and utilization of the biomass energy are developed in directions of high efficiency and cleanness, wherein a biomass liquefaction process is an important part. The existing biomass liquefaction process are mainly divided into indirect liquefaction and direct liquefaction, wherein the direct liquefaction is to directly liquefy a biomass from a solid to a liquid under a suitable temperature and a suitable pressure by carrying out hydrolysis and supercritical liquefaction or introducing hydrogen, inert gas and the like under the action of a solvent or a catalyst. The biomass direct liquefaction process mainly comprises pyrolysis liquefaction, catalytic liquefaction, pressurized hydroliquefaction and the like, wherein especially products of pressurized hydroliquefaction have high yield and good quality, but the pressurized hydroliquefaction has harsh high-pressure liquefaction reaction conditions, and the pressurized hydroliquefaction further comprises very complex working procedures, such as solid material drying, crushing, slurry preparing, heating, pressurizing, reacting, separating and the like. For example, Chinese patent CN103242871A discloses a heavy oil and biomass hydrogenation co-liquefaction treatment process, and the process comprises the steps of pre-crushing a dried biomass to be 40-100-mesh, mixing the pre-crushed biomass of 40-100-mesh with a heavy oil to form a slurry, adding a catalyst and a vulcanizing agent into the slurry, placing the mixture in a slurry bed hydrogenation reactor to undergo a hydrogenation and thermal cracking reaction, wherein the reaction is controlled to be carried out under a temperature of 370-430 DEG C. and a partial pressure of hydrogen of 4-8 MPa, and fractioning the reaction product, thereby obtaining a bio-oil and coke.
Although the above-mentioned process can improve the conversion rate of the biomass to 90 wt % or above and the yield of an oil phase to 70 wt % or above, the process is relatively higher in reaction temperature and relatively smaller in partial pressure of hydrogen, thereby causing relatively lower efficiency of reactions, such as hydrolysis, cracking, hydrogenation and the like, finally causing a relatively larger rate of coke formation, and definitively causing a low yield of a liquid phase. Therefore, a technical problem to be urgently solved by those skilled in the art is to improve the existing biomass liquefaction process so as to overcome the defects of low reaction efficiency and a large rate of coke formation.